Method of eliminating reradiation



Dec. 28 1937. GOTHE 2,103,358

- METHOD OF ELIMINATING RERADIATION 7 Filed March 15, 1935 INVENTOR.ALBRECHT GOTHE ATTORNEY.

Patented Dec. 28, 1937 METHOD OF ELHWINATING RERADIATION Albrecht Gothe,Berlin, Germany, assignor t0 Telefunken Gesellschaft fiir DrahtloseTelegraphic in. b. H., Berlin, Germany, a corporation of GermanyApplication March 13, 1935, Serial No. 10,787

, In Germany March 26, 1934 1 6 Claims.

It has been known for a long time that the fieldsyof antennae aredistorted by neighboring electrical conductors if radio frequencycurrents 'of substantial strength are flowing through the latter. Amongsuch conductors may be men- .tioned primarily the masts of antennaeconsisting of metal and the staying or guy means thereof. If the saidconductors happen to be in resonance with the working wave or nearly so,they act as reradiators and areliable to alter considerably theradiation diagram of the antenna. At-' tempts are often made to curethis condition by marked detuning. The guying cables or wires aresubdivided by insulators. The masts are insulated or grounded, and bythe interposition of impedances between the base of the mast and theground, they are caused to assume a natural period which is as remotefrom the working wave as is feasible. It has also been suggested to varythe natural wave or period of metallic conductors by the use of tunedring coils which are placed around the conductor, or by the parallelconnection of capacities to the whole conductors or parts thereof.

As long as the length of the conductors liable to act as reradiatorsdoes not exceed one-quarter wave-length, substantially, the eliminationof reradiation is comparatively simple. But, the situation is aggravatedmore if the length of the reradiators is of a magnitude of one orseveral waves. Conductors which are excited by high harmonics, as iswell known, have complex radiation diagrams. The ways and meanshereinbefore mentioned tothe end of curing reradiation will then beeffective only if very definite presuppositions are fulfilled.

When the width of the reradiators is very small compared with the lengththereof and the operating wave, there is but one direction of currentwhich coincides with the longitudinal dimension of the conductor. Thiscondition ceases as soon as the conductor assumes the form of a plane orsurface; in other Words, if it has a width that is no longer negligiblysmall in contrast to the wave length. This will happen, for instance,whenever short waves are transmitted from vessels or the like, such asmarine vessels or ships, airplanes, etc. The radio frequency currentdistribution over such surfaces in the majority of cases is determinableonly with difiiculty or not at all; otherwise marked reradiation isobserved, which has the result that the antenna radiation varies verymarkedly in different directions.

According to this invention, the reradiation of such surfaces is to beobviated by interconnect ing points presenting substantial radiofrequency potential differences by means of chain conductors or filters.The range of transmission of such filters is so adjusted that theworking wave encounters the lowest possible impedance.

One fundamental circuit diagram is illustrated in the drawing. Referringto the same, F represents a surface which is excited by a radiofrequency radiator St so that radio frequency voltage differences areset up between the points Pl, P2, P3, P4. By the filter systemcomprising C and L elements, the said points are connected with oneanother so that the potential differences are eliminated. The particularconnection of the filters in the present instance is immaterial, infact, it may be established also in a Way other than that shown in thedrawing. If the voltage distribution over a surface is not known, then aplurality of chain conductors or filters should be employed, while theconnecting points should be chosen not over one-half wave length apart.

Frequently it is not desirable, especially in the case of vehicles orvessels, to cover the face of the surface excited by radio frequencieswith chain conductors or filters because they will then offer addedresistance to the travel or motion of the vessel; not to mention thefact that they are endangered or subject to damaging. According to thisinvention, therefore, the filters are disposed upon the other face ofthe surface in question. However, the connecting points or terminals ofthe filters should be disposed upon the face turned towards the radiofrequency radiator; hence, short connecting leads should be broughtthrough holes in the surface.

If there are several working waves for which reradiation by the surfaceis to be avoided, then, according to this invention either the ranges oftransmission of the filters are chosen adequately wide, if the operatingwaves are close together, or else several filters for differentfrequency ranges are installed.

The filters, as well known in the art, are built up of concentrated(lumped) inductances and capacities. From the viewpoint of simplicity ofinstallation in the neighborhood of the electrically conducting surface,it will be found desirable to provide electrical shielding for thefilter so that its electrical properties will not be a function of theposition of the surface. For the purpose of facilitating installation,it would be advantageous to make the electrical shielding which coversthe filter flexible.

It is not necessary that the filter should comprise only concentratedinductances and capacities. Indeed substantial parts thereof couldconsist also or reside in the leads brought to the adjoining connectingpoints or terminals. It is likewise feasible to use a cable, whoseelectrical length is equal to the working wave, as a filter, for betweenthe ends of such a cable there exists no voltage difference,-in otherwords, it acts like an electric short circuit.

What is claimed is: V V

1. The method of eliminatingreradiation from an electrical conductingsurface which is excited by a radio frequency radiator, which comprisesshort circuiting points on said surface facing said radiator whichpresent between said points substantial radio frequency voltagedifferences at the frequency of the operating wave of said radiator. q

2. In combination, an antenna adapted to raldiate waves, a conductor inthe path of said waves, and a path of low impedance to the energy of thewaves radiated by said antenna connecting together points on saidconductor which face said antenna and whose spacing does not exceedone-half the length of the desired wave and which have substantial radiofrequency potential differences between said points at the frequenciesof the waves radiated by said antenna.

3. A system in accordance with claim 2, characterized in this that saidlow impedance means comprises one or more filters.

4. In combination, an antenna adapted to radiate waves, a conductorphysically separated from and substantially parallel to said antenna andlocated in the path of said waves, and a path of low impedance to theenergy of the waves radiated by said antenna connecting together pointson the surfaces of said conductor facing said antenna and which havesubstantial radio frequency potential differences between said points"at the frequencies of the waves radiated by said antenna foreliminating reradiation from said conductor.

5.A system inaccordance with claim 4, characterized in, this that saidpath comprises one or more filters located on the side of said conductoropposite said surface.

6. In combination, an antenna adapted to radiate waves, a conductor inthe path of said waves, said conductor having appreciable length withregard to its thickness, and a path of low impedance to the energy ofthe waves radiated by said antenna connecting together two points onsaid conductor which face said antenna and whose spacing does not exceedone-half the length of the desired wave and which points havesubstantial radio frequency potential differences between them at thefrequencies of the waves radiated by said antenna.

ALBRECHT GO'IHE.

